Strict ontogenetic control vs. environmental plasticity: the stability of colour morphs in the Common Wall Lizard

Whether the complex colour polymorphisms of lizards are governed by rigid genetic control or by the type of phenotypic plasticity recently discovered in side-blotched lizard ( Uta stansburiana ) remains a critical question for understanding the maintenance of these systems. In this study, we utilized a four-year capture-recapture dataset to investigate if adult common wall lizards ( Podarcis muralis ) exhibit similar plastic transitions or follow a fixed developmental program. Using standardized digital photography and Residual Randomization Permutation Procedures (RRPP), we quantified Hue and Saturation variation across 167 adult individuals (216 transition events). Our results reveal an exceptional degree of categorical stability, with 97.7% of individuals retaining their discrete colour morph among captures; the rare transitions observed were exclusively unidirectional, involving initially white individuals acquiring pigmentation. While individual identity accounted for over 45% of the spectral variance, low repeatability coefficients (ICCs < 0.13) indicate high intra-morph chromatic uniformity. Phenotypic trajectory analysis demonstrated that as individuals grow, morphs significantly diverge in both colour intensity and direction. Notably, the yellow morph follows a unique, morph-specific maturation path, suggesting a canalized developmental program that enhances signal clarity with age. Unlike the reversible hormonal plasticity documented in U. stansburiana , the P. muralis system appears driven by a fixed ontogenetic commitment. These findings suggest that this polymorphism is maintained by a robust genetic architecture where adult maturation might serve to minimize cross-talk among socio-sexual signals, highlighting the analysis of adult ontogenetic trajectories as a vital practical tool for deciphering the evolution of complex biological polymorphisms.